1. Field of the Invention
The present invention relates generally to a combined cycle power plant, and more specifically to a power plant configuration for efficient combined heat and power production in a small size.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
A power plant is used to produce electricity for use in the general area or transmitted to far away areas where demand is high and production is low. Electric producing power plants are of the type such as a nuclear plant, a coal burning plant or a natural gas burning plant. Coal burning power plants are not desirable because of the pollutants discharged from the exhaust. Natural gas burning power plants are favorable because they are cleaner than the coal burning plants.
The design of an electricity producing power plant is directed to producing the most efficient electrical power. Thus, the most highly efficient power plants tend to be very large power plants that are a permanent fixture in an area. Because of the very large size, these large power plants can produce enough electrical energy to be distributed to vary large areas.
The idea of using waste heat for increased steam generation in industry has been around for many years. The progressive increase in fuel costs, the need to capture heat from various industrial processes and the increasingly stringent environmental regulations has created the need for using waste heat to its fullest potential.
In the power industry, the waste heat from one power system such as a gas turbine engine can serve as the heat source for a steam turbine cycle. Such a system is referred to as a combined cycle and can reach overall electrical power cycle efficiency to nearly 60%. A combined cycle power plant integrates two or more thermodynamic power cycles to more fully and efficiently convert input energy to work or power. With the advancements in reliability and availability of gas turbine engines, the term combined cycle power plant usually refers to a system that includes a gas turbine engine, a heat recovery steam generator (HRSG) and a steam turbine. Thermodynamically, this implies the joining of a high temperature Brayton gas turbine engine cycle with a moderate and low temperature Rankine cycle where the waste heat from the Brayton cycle exhaust is used to heat input to the Rankine cycle. Where the heat recovery steam generator supplies at least part of the steam for a process, the application can be referred to as cogeneration.
A simple combined cycle power plant includes a single gas turbine engine with an electric generator, a heat recovery steam generator (HRSG), a single steam turbine and electric generator, and a condenser and auxiliary systems. FIG. 1 shows a prior art combined cycle power plant with a gas turbine engine, a HRSG and a steam turbine. The FIG. 1 power plant includes a gas turbine engine with a compressor 12, a combustor 13 and a turbine 14 that drives a first electric generator 11, where the turbine exhaust is delivered to a HRSG 15 that includes a stack 22 for discharge of the exhaust and a steam turbine 16 that drives a second electric generator 17. The HRSG includes a condenser 18, a condensate pump 19, a de-aerator 20 and a boiler feed water pump 21.
The modern 250 MW natural gas fired combined cycle power plant is the most economic option for new electric power production. The power plant efficiency is around 58% for electricity at the power plant, the natural gas fired plant is less than 50% CO2 production when compared to a coal fired power plant, and the power plant is very reliable with power produced anytime and with 50,000 plus hours of component life. However, some major disadvantages exist in this type of power plant. Of the fuel energy input, 32% of the energy is wasted heating rivers or the atmosphere from the steam condenser cooling. The condenser cooling heat from the power plant cannot be reused because of the far location of the plant to any potential users of the heat. For example, the heat could be used to heat a building but is not feasible because the heat would cool to atmospheric temperature from the long distance carried from source to end user. Also, more than 7% of the electricity produced is wasted in transmission line losses. Because they are so large, they produce a large amount of electricity which requires a large electrical grid and long power lines to transmit the power to relatively far away locations. Thus, the loss of electrical energy due to the long transmission line loses.